Zirconia sintered bodies containing a small amount of Y2O3 in a solid solution state as a stabilizer have high strength and high toughness and are hence extensively utilized as materials for machine structures, such as cutting tools, dies, nozzles, and bearings, and materials for the living body, such as dental materials. In the case of dental materials, not only mechanical properties, i.e., high strength and high toughness, but also optical properties, i.e., translucency and color tone, are required from an aesthetic standpoint.
Single crystals of zirconia give a sense of translucency, and single-crystal zirconia containing about 10 mol % yttria (cubic zirconia), which is used as jewelry and the like, has conventionally had a problem that the strength thereof is exceedingly low. On the other hand, it is known that ordinary zirconia sintered bodies, which are polycrystalline objects, do not give a sense of translucency. It is known that the lack of translucency is due to the light scattering caused by voids present between the crystal grains and within the grains. Investigations have hence been made hitherto on techniques for imparting translucency to a polycrystalline zirconia sintered body by diminishing voids, i.e., by increasing the density of the sintered body.
For example, patent document 1 discloses translucent zirconia containing 2 mol % or more Y2O3 and 3-20 mol % TiO2. However, this translucent zirconia has had a problem concerning strength because this zirconia contains a large amount of TiO2 incorporated in order to impart translucency.
Patent document 2 discloses a zirconia sintered body having a sintered-body density of 99.8%, which has a composition including 3 mol % Y2O3 and 0.25 wt % Al2O3 and has translucency. It has been reported that this sintered body has a total light transmittance with respect to visible light of 49% (thickness, 0.5 mm) However, this sintered body is a sintered body obtained by pressure sintering using hot isostatic pressing (HIP), and sufficient translucency has not been obtained in sintered bodies obtained by normal-pressure sintering.